Over the years, rubber compounders have used various materials in rubber to obtain the desired processing characteristics, ultimate properties of the finished product or cost control. Such materials may be classified as vulcanizing agents, accelerators, accelerator activators and retarders, age resistors, processing aids, reinforcing pigments and resins, inert fillers and special purpose materials. With the ever-present demands to improve the processing characteristics, properties and costs, rubber compounds are forever on the lookout for new materials for use in rubber.
U.S. Pat. No. 3,446,861 discloses a catalyst for the selective cyclodimerization of 1,3-butadiene. The catalyst comprises (1) iron salts or iron complexes, (2) an organometallic reducing agent and (3) certain ligands containing nitrogen. Representative of such ligands include biacetyl-bis-anil, biacetyl-bis-(4-hydroxyanil) and biacetyl-bis-(4-ethoxyanil).
Quite surprisingly, it has been discovered that use of bis anil compounds improve properties of rubber when added.